Mortality associated biological age improves independently of weight loss after bariatric surgery

Obesity increases the risk of common diseases and mortality, placing a significant burden on our aging society. Bariatric surgery results in significant weight loss; however, the amount of associated health gain is currently less studied, particularly in the first two years. We modelled mortality-associated biological age according to established blood markers in a prospective cohort of 505 patients that underwent bariatric surgery. The difference between biological age and chronological age (age acceleration) as a molecular marker of health gain was evaluated at different time points with mixed effects models. At baseline, biological age acceleration was positively correlated to higher smoking exposure as well as increased body mass, particularly in males. Twelve months after surgery, patients were on average 5.55 years younger (slope and 95% confidence intervals (95% CI): -5.55 [-6.12; -4.97]) which remained stable until 24 months. When adjusted for changes in body mass index over time, the effect seizes decreased to 3.32 years younger age at 12 months post-surgery (slope and 95% CI: -3.32 [-4.26; -2.37]), indicating an age-rejuvenating effect - more pronounced in men - beyond weight loss. Individual markers such as glucose and C-reactive protein levels as well as blood cell counts contributing to biological age computation showed a generally more favorable change after surgery. In conclusion, biological age was markedly reduced in patients undergoing bariatric surgery resulting in a 40-50% reduction in expected mortality after two years, particularly in men. Our findings support the use of biological age as a clinically meaningful, patient-centered marker of treatment success after bariatric surgery.